Combination light-emitting diode (LED) silicon photo-detector components are commonly used as sensor units. A commercially-available component places the LED and detector side by side, both facing in the same direction from a common active surface, with the LED when pulsed emitting a narrow cone of light in one direction and the adjacent detector generating current when illuminated from the same direction. The unit is commonly used to sense the presence of a reflecting surface over the LED, by reflecting some of the intercepted radiation back toward the detector.
There are applications employing a large number of such combination units, which applications require selective activation by a controller of one or more units. Moreover, it is sometimes desirable to align the multiple units near or adjacent one another to form an array, and a problem then arises of minimizing the effect of scattered reflected radiation on detectors remote from the emitting LED. When large numbers of such combination units are present in a system, the number of connections from the controller to the units may become excessive.